Agarwood trade has been growing rapidly due to its active ingredients composed of volatile substances, which are widely used in the cosmetics and pharmaceuticals. However, the formation time of agarwood in nature is quite long and little is known about its formation agents and mechanisms in planted Aquilaria crassna trees. In this study, biological, chemical and mechanical treatments were applied to 5-, 8-, and 11-year-old A. crassna plantations in north central, Vietnam. Agarwood samples were collected at 1 and 2 years after treatment. Oil content (O c ) in dry wood of A. crassna and sesquiterpene content in extracted oil were analyzed using hydrodistillation method and gas chromatography-mass spectrometry. The results indicated that 1 year after treatment, control (no treatment) and mechanical treatment (nails hammered to tree stems) had highest O c (0.061-0.079 %) but lowest sesquiterpene content (2.1-7.1 %). Chemical treatment (mixture of acid sulfuric and sodium methyl bisulfate) had lowest O c (0.038-0.039 %) but highest sesquiterpene content (15.8-20.8 %). While, 1 year after treatment biological treatments had O c of 0.050-0.077 % and sesquiterpene content of 2.4-11.1 %. Two years after treatment, control still had lowest sesquiterpene content (3.2-7.0 %), while highest content (13.9-44.2 %) belonged to biological treatment (a mixture of fungi Phialophora spp. and Fusarium spp.). There was a total of 56 sesquiterpenes found in extracted oil from wood samples in biological treatments, which included eight highly commerciallyvaluable sesquiterpenes on international trade. Biological treatment with a mixture of fungi P. spp. and F. spp. should be encouraged to apply to 11-year-old A. crassna plantation, which resulted in highest sesquiterpene content (44.2 %).

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Fertilizers (nitrogen/N, phosphorous/P, and potassium/K) have been widely applied to increase the productivity of forest plantation, especially in poor soils. This study was to test the effects of fertilization at planting and additional fertilization in the following two years on growth and aboveground biomass (AGB) of a 30-month old plantation of Acacia mangium in Northeast Vietnam. There were four treatments including (1) 1 kg compost/tree at planting and 0.2 kg NPK (16:16:8)/tree/year in the following two years (IC-A-NPK), (2) 1 kg compost/tree at planting and 0.2 kg P (16.5% P2O5) + 0.1 kg K (60% K2O)/tree/year in the following two years (IC-A-PK), (3) 1 kg compost + 0.2 kg NPK/tree at planting and 0.2 kg NPK/tree/year in the following two years (IM-A-NPK), and (4) 1 kg compost + 0.2 kg NPK/tree at planting and 0.6 kg P + 0.1 kg K/tree/year in the following two years (IM-A-PK). The results indicated there was no significant effect of fertilization at planting and additional fertilization on diameter at breast height (DBH), basal area, and AGB between IC-A-NPK (DBH of 8.9 cm, basal area of 7.4 m 2 ha -1 , and AGB of 37.8 Mg ha -1 ) and IM-A-NPK (DBH of 10.1 cm, basal area of 9.2 m 2 ha -1 , and AGB of 47.5 Mg ha -1 ). Meanwhile, DBH (9.6 cm), basal area (8.6 m 2 ha-1 ) and AGB (44.2 Mg ha -1 ) in IM-A-PK were significantly higher than that in IC-A-PK (DBH of 8.4 cm, basal area of 6.4 m 2 ha -1 , and AGB of 31.6 Mg h -1 ). It was concluded that fertilization at planting of both compost and NPK is not required for A. mangium plantation. While additional fertilization of phosphorus should be applied for higher productivity.

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